The present invention relates to a control system for controlling an electromagnetically operated valve, and more particularly to an electromagnetic valve control system which is capable of executing a soft landing of a movable member onto an electromagnet in a valve open/close control.
In recent years, there have been proposed various electromagnetic valve operating systems that employ an electromagnetic actuator comprised of a movable member, a pair of electromagnets and a pair of springs so as to reciprocatingly operate intake and exhaust valves of an internal combustion engine. Generally, it is preferable that a movable member of such a valve operating system is softly landed on an electromagnet while ensuring a required motion performance. A Japanese Patent Provisional Publication No. (Heisei)11-159313 discloses a landing method for softly landing a movable member on an electromagnet in an electromagnetic valve operating system. Such soft landing in this system is achieved by temporally switching off the electromagnet during a period between a switch-on moment of the electromagnet and the landing moment of the movable member. Further, in order to realize a further accurate landing control of an electromagnetic valve unit including a valve and an electromagnetic actuator, there has been proposed a control method employing a characteristic representative of a vibration system of the electromagnetic valve unit.
However, the characteristic of the vibration system of the controlled electromagnetic valve unit is varied according to an operating condition. Particularly, a friction in the electromagnetic valve unit is largely affected by a temperature since the friction largely depends on a characteristic of lubricating oil whose viscosity is varied according to the change of temperature. Therefore, it is difficult to stably execute a required landing control only by a preset characteristic representative quantity.
It is therefore an object of the present invention to provide a control system which further certainly executes a soft landing control of an electromagnetic valve unit by varying a model constant of the vibration system of a controlled electromagnetic valve unit according to an actual operating condition.
An aspect of the present invention resides in a valve control system which comprises an electromagnetic valve unit and a controller. The electromagnetic valve unit comprises a valve, a pair of electromagnets arranged in spaced relationship from one another in axial alignment with the valve so as to form a space, a movable member axially movably disposed in the space between the electromagnets and interlocked with the valve, a pair of springs biasing the movable member so as to locate the movable member at an intermediate portion of the space when both of the electromagnets are de-energized. The controller is connected to the electromagnetic valve unit and executes an initialization control for moving the movable member to a start position by repeatingly energizing the electromagnets according to a natural frequency of a vibration system of the electromagnetic valve unit. The controller detects amplitudes of oscillation of the movable member during the initialization control, calculates an increase-degree of the detected amplitudes, and estimates a friction quantity of the vibration system on the basis of the calculated increase-degree.